Lamb Wave Interaction with Impact-induced Damage in Aircraft Composite: Use of the A0 Mode Excited by Air-coupled Transducer

Abstract

A novel technique has been experimented involving the use of an air-coupled transducer to excite Lamb mode in composite material, a pinducer to pick-up local response and a turn-table set-up to reveal impact damage-induced anisotropy.

So, a fundamental antisymmetric A ₀ Lamb mode has been excited under unusual conditions. Its efficiency for detecting impact-induced damage in a multilayered thin quasi-isotropic carbon–epoxy composite laminate has been demonstrated and the knowledge on the A ₀ Lamb mode interaction with the damage has been improved using an original mapping.

Some material characteristics have been obtained. Intrinsic material attenuation of this guided mode at a frequency of 370 kHz and a frequency-thickness product of 740 kHz mm has been assessed and in-plane energy distribution of the A ₀ mode has been mapped, revealing a relatively directive acoustic field. However, the composite material exhibits slightly anisotropic acoustic behaviour due to a lack of fibres in certain directions. Interactions between the A ₀ mode and multidelamination of the critical area were also investigated. In-plane mappings of the ultrasonic field have revealed two main phenomena: attenuation and scattering due to damage. Splitting of the ultrasonic wave was observed, creating a region of geometric shadow where attenuation occurs. It is shown on the mappings that the energy lost in this direction of propagation appears in other directions. An increase in the received energy was detected in certain directions, showing that the damage can be considered as a soft scattering centre.

Keywords

ultrasonic air-coupled transducer pinducer lamb waves multilayered composite damage delamination dispersion curves

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